Due to their promising development in the medical field as radiopaques (contrast agents for X-rays) or as oxygen carriers in blood substitutes, perfluoroalkyl bromides have formed the subject in recent years of many patents relating to their synthesis from perfluoroalkyl sulphochlorides R.sub.F SO.sub.2 Cl (EP 0,298,870 and 0,429,331), from perfluoroalkyl iodides R.sub.F I (JP 85-184033, EP 0,428,039, EP 0,450,584, EP 0,515,258 and EP 0,519,808) or from hydrogenoperfluoroalkanes R.sub.F H (US 3,456,024 and EP 0,549,387) as well as to their purification (EP 0,513,783). The processes described in these patents are essentially targeted at the manufacture of perfluoroalkyl bromides which are liquid at room temperature and in particular at that of n-perfluorooctyl bromide C.sub.8 F.sub.17 Br (known under the abbreviation PFOB).
Among these known processes, the most direct route for obtaining perfluoroalkyl bromides is obviously that described in Patents EP 0,450,584 and 0,515,258 which consists of the thermalbromination in the gas phase of the corresponding iodides R.sub.F I which are available in industrial quantities. An industrial plant for the manufacture of a perfluoroalkyl bromide must comprise, downstream of the reactor, various devices which make it possible to recover the iodine by-product and to isolate the perflUoroalkyl bromide by means of unit operations such as reduction of iodine, neutralization, separation, neutralization/washing, and the like.
When the desired perfluoroalkyl bromide is liquid at room temperature, especially PFOB, the melting point of which is 6.degree. C., these various devices are very simple and inexpensive appliances because they do not need to be traced or to have a double heating jacket.
An industrial plant designed with such equipment for the manufacture of a liquid bromide such as PFOB cannot be used, without significant investment and modification, for manufacturing a solid bromide such as perfluorodecyl bromide (hereinafter PFDB), the melting point of which is 55.degree. C., the starting perfluorodecyl iodide having a melting point of 65.degree. C.